Configuration and resource allocation for downlink demodulation reference signals

ABSTRACT

According to one aspect, a network node is provided. The network node includes processing circuitry configured to allocate resources for a reference signal signaling for a first wireless device, the allocated resources configured to separate, in a slot, at least one transmission layer of the first wireless device from at least one transmission layers of a second wireless device by at least one of scheduling the first wireless device and second wireless device different reference signal ports that are separated by using the same resource elements and different CDM codes, scheduling the first wireless device and second wireless device at least one shared reference signal port using the same resource elements and CDM code, and scheduling the first wireless device and second wireless device on different reference signal ports that are separated by FDM using different resource elements and the same CDM codes.

TECHNICAL FIELD

Wireless communication and in particular, reference signal configurationand allocation.

BACKGROUND

5^(th) Generation (5G) wireless communication technology, also referredto as New Radio (NR) technology, represents the next step in thewireless communication industry where NR related products are currentlybeing developed worldwide.

In NR, the demodulation reference signal (DMRS) is used in both thedownlink (DL) and the uplink (UL). The DMRS is used to help the wirelessdevice or network node (e.g., gNB) decode the DL or UL traffic/controlchannels, respectively. The DMRS can be single-symbol or double-symbolbased. For single-symbol based DMRS, the DMRS resource can be mapped toa single OFDM (Orthogonal Frequency Division Multiplexing) symbol orseveral (up to 4) separated OFDM symbols. For double-symbol based DMRSthe minimum resource for DMRS consists of two consecutive OFDM symbols,and the total number of OFDM symbols for DMRS in a slot is either 2 or4. FIG. 1 shows examples patterns for single-symbol based anddouble-symbol based DMRS configuration.

In the frequency domain, the 12 sub-carriers in an OFDM symbol aredivided into 2 or 3 CDM (Code Division Multiplexing) groups. Type 1 DMRShas 2 CDM groups while type 2 DMRS has 3 CDM groups. In FIG. 2, theresource elements (REs) in the same hatchings style belong to the sameCDM group.

Both type 1 and type 2 DMRS support multiple DMRS ports through FDM(Frequency Division Multiplexing) and CDM (Code Division Multiplexing).For single-symbol based, type 1 DMRS, the length-2 OCC (Orthogonal CoverCode, i.e., one example of a CDM code) is used in the frequency domainin each CDM group, so each CDM group can support 2 DMRS ports. With 2CDM groups, the maximum number of 4 DMRS ports can be supported asillustrated in FIG. 3 that illustrates DMRS ports for type 1 DMRS whererespective CDM groups are represented by respective hatching styles.Similarly, for double-symbol based, type 2 DMRS, the length-2 OCC isused in frequency and time domains in each CDM group, so each CDM groupcan support 4 DMRS ports. With 3 CDM groups and double-symbol based, themaximum number of 12 DMRS ports can be supported as illustrated in FIG.4 that illustrates DMRS ports for type 2 DMRS where respective CDMgroups are represented by respective hatching styles.

Both DL and UL DMRS are configured for each wireless device through RRC(Radio Resource Control) messages. For DL DMRS, DMRS type, the maximumnumber of OFDM symbols for DL front loaded DMRS (If the value is 1, onlysingle-symbol based DMRS is used. If the value is 2, both single-symbolbased DMRS and double-symbol based DMRS can be used depending on thescheduling control information), the presence of additional DMRS in aslot, and two scrambling initialization IDs (i.e., scrambling IDs) areconfigured by higher layer signalling, where each scrambling ID maycorrespond to one or multiple scrambling sequences. For a DMRSconfiguration, certain DMRS resources are allocated to a wireless devicefor a specific PDSCH (Physical Downlink Shared Channel) transmission tothe wireless device. The DMRS resource allocation is informed to thewireless device through downlink control information (DCI) format 1_1,which carries information such as the number of DMRS CDM groups withoutdata, DMRS ports, and the number of front loaded DMRS symbol (one ortwo). While the DMRS ports in the DCI format 1_1 are specific for thewireless device, the number of CDM groups and the number of front loadedDMRS symbols may not be specific for the wireless device.

A DMRS sequence may be generated using known techniques, for exampleaccording to the assigned DMRS ports and the configured higher-layerparameter scramblingID0 or scramblingID1 and mapped onto the DMRSresources. The assigned DMRS ports and the scrambling ID may set theinitial state of shift registers in generating the Gold codes used ingenerating DMRS sequences.

When the network node transmits DL traffic to wireless devices, thetransmission can be in the form of SU-MIMO (single-user multiple-inputand multiple-output) or MU-MIMO (multi-user MIMO). For SU-MIMO, each DLPRB (Physical Resource Block) is used by a single wireless device. Ifthe rank is greater than 1, the multiple layers for the wireless devicemay be separated by orthogonal DMRS ports. Thus, the wireless device canidentify the DMRS for each layer and perform DL channel estimationaccordingly. For MU-MIMO, each DL PRB (Physical Resource Block) can beshared by multiple wireless devices at the same time. Now thetransmission layers can be separated by orthogonal DMRS ports andnon-orthogonal scrambling initialization IDs. Similar to SU-MIMO, eachwireless device identifies the DMRS for all layers belonging to it andperform DL channel estimation accordingly.

As previously described, two DMRS scrambling initialization IDs can beconfigured for each wireless device. For each PDSCH transmission for thewireless device, the network node determines which ID(s) may be includedin the Downlink Control Information (DCI). In every DL TTI, the networknode determines which DMRS port(s) may be allocated for a wirelessdevice irrespective if SU-MIMO or MU-MIMO is being implemented.

The algorithms that determine the scrambling initialization IDs to beconfigured for a wireless device and determine which DMRS port(s) andscrambling initialization ID(s) to be allocated for a wireless devicecan impact the network performance, which can be illustrated by thefollowing examples:

Example 1: A wireless device is configured with type 1, single-symbolbased DL DMRS. For a SU-MIMO PDSCH transmission with rank of 2, thenetwork node may need to assign two DMRS ports for the wireless device.If ports (1000, 1001) are allocated for the wireless device, thisallocation can result in degraded channel estimation performancecompared to the allocation of ports (1000, 1002) since the CDM separatedports (1000, 1001) may lead to larger channel estimation error comparedto FDM separated ports (1000, 1002). On the other hand, ports(1000,1002) has double RS overhead compared to using ports (1000,1001).

Example 2: Considering a MU-MIMO transmission where all the co-scheduledwireless devices are configured with the same scrambling initializationIDs. It is assumed that all wireless devices are configured with type 1,double-symbol based DL DMRS. In this case, there are up to 8 differentDMRS ports. If all MU-MIMO layers are separated by orthogonal DMRS portsonly (same scrambling ID for all ports in the same CDM group), the maxnumber of MU-MIMO layers is limited to 8. If the network node decides touse scrambling initialization ID to separate DMRS (using pseudoorthogonal separation) and randomly selects two wireless devices toshare the same DMRS port(s), the DL channel estimation performance canbe quite poor if the two wireless devices are not well separatedspatially. Even if the network node tries to make the spatially wellseparated wireless devices to share the same DMRS port(s), thosewireless devices may not have different scrambling initialization IDs touse due to bad scrambling initialization ID configuration.

Hence, one issue with existing systems relates to the scheduler at thenetwork node and how the scheduler assigns these ports and scramblingIDs (i.e., the use of orthogonal ports or pseudo orthogonal portsrespectively) to attempt to maximize the wireless device throughputand/or the network performance (such as the total throughput across allscheduled wireless devices) which is related to the total number oftransmitted layers in a slot. Another issue in existing systems relatesto how to maximize the channel estimation performance using this portand scrambling ID selection.

SUMMARY

The instant disclosure solves at least a portion of at least one problemassociated with existing systems by providing a DL DMRS configurationand resource allocation that may enable wireless devices to obtainbetter downlink channel estimation than, for example, existing systems,and may allow more layers to be supported for DL MU-MIMO. This may helpachieve better downlink throughput.

Some embodiments advantageously provide a method, network node, wirelessdevice and system for reference signal configuration and allocation.

According to one aspect of the disclosure, a network node is provided.The network node includes processing circuitry configured to: allocateresources for a reference signal signaling for a first wireless device,the allocated resources configured to separate, in a slot, at least onetransmission layer of the first wireless device from at least onetransmission layers of a second wireless device by at least one of:scheduling the first wireless device and second wireless devicedifferent reference signal ports that are separated by using the sameresource elements and different code division multiplexing, CDM, codes,the first wireless device and second wireless device having associatedscrambling sequences, scheduling the first wireless device and secondwireless device at least one shared reference signal port using the sameresource elements and CDM code, the first wireless device and secondwireless device having different scrambling sequences, scheduling thefirst wireless device and second wireless device on different referencesignal ports that are separated by frequency division multiplexing, FDM,using different resource elements and the same CDM codes, the first andsecond wireless device having associated scrambling sequences, andscheduling the first wireless device and second wireless device ondifferent reference signal ports that are separated through both FDM andCDM by using different resource elements and different CDM codes, thefirst wireless device and second wireless device having associatedscrambling sequences.

According to one embodiment of this aspect, the first wireless deviceand the second wireless device having the at least one shared referencesignal port are part of a wireless device sub-group, the wireless devicesub-group meeting at least one predefined spatial condition. Accordingto one embodiment of this aspect, at least one predefined spatialcondition includes a spatial metric associated with each wireless devicewithin the subgroup that meets a predefined criterion with respect toall other wireless devices in the same subgroup. According to oneembodiment of this aspect, the spatial metric is a measure of an angleof arrival, AoA, (or equivalently, angle of departure AoD) between awireless device and a plane of an antenna array of the network node.

According to one embodiment of this aspect, the spatial metric is ameasure, possibly a real or complex valued scalar, or a complex valuedvector or matrix, of spatial channel—from the transmitter antennas ofthe network node to the receiver antennas of a wireless device within asubgroup with respect to the network node. According to one embodimentof this aspect, the predefined criterion is associated with a differenceof spatial metrics between two wireless devices that is greater than apredefined threshold. According to one embodiment of this aspect, thepredefined criterion is associated with an absolute value of an innerproduct of the normalized spatial metrics of any two wireless devicesthat is less than a predefined threshold.

According to one embodiment of this aspect, the allocated resourcesprovide for multi-user multiple-input multiple-output, MU-MIMO,transmission. According to one embodiment of this aspect, the referencesignal ports corresponds to a rank of the transmission to a firstwireless device. According to one embodiment of this aspect, theprocessing circuitry is further configured to determine a number ofphysical resource blocks, PRBs, allocated to the first wireless device,the scheduling of the at least one shared reference port to the firstwireless device and second wireless device being based on the determinednumber of PRBs. According to one embodiment of this aspect, the firstwireless device is scheduled for a reference signal port combination forone selected from a group consisting of: a one front-load referencesignal symbol configuration; and a two front-load reference signalsymbol configuration. According to one embodiment of this aspect, theprocessing circuitry is further configured to: allocate resources forreference signal signaling for a plurality of wireless devices includingthe first wireless device, the allocated resources configured toseparate, in a slot, at least one transmission layer of each of theplurality of wireless devices from each other, respectively.

According to another aspect of the disclosure, a method for a networknode is provided. Resources for a reference signal signaling for a firstwireless device are allocated. The allocated resources configured toseparate, in a slot, at least one transmission layer of the firstwireless device from at least one transmission layers of a secondwireless device by at least one of: scheduling the first wireless deviceand second wireless device different reference signal ports that areseparated by using the same resource elements and different codedivision multiplexing, CDM, codes, the first wireless device and secondwireless device having associated scrambling sequences, scheduling thefirst wireless device and second wireless device at least one sharedreference signal port using the same resource elements and CDM code, thefirst wireless device and second wireless device having differentscrambling sequences, scheduling the first wireless device and secondwireless device on different reference signal ports that are separatedby frequency division multiplexing, FDM, by using different resourceelements and the same CDM codes, the first and second wireless devicehaving associated scrambling sequences, and scheduling the firstwireless device and second wireless device on different reference signalports that are separated through both FDM and CDM by using differentresource elements and different CDM codes, the first wireless device andsecond wireless device having associated scrambling sequences.

According to one embodiment of this aspect, the first wireless deviceand the second wireless device having the at least one shared referencesignal port are part of a wireless device sub-group, the wireless devicesub-group meeting at least one predefined spatial condition. Accordingto one embodiment of this aspect, at least one predefined spatialcondition includes a spatial metric associated with each wireless devicewithin the subgroup that meets a predefined criterion with respect toall other wireless devices in the same subgroup. According to oneembodiment of this aspect, the spatial metric is a measure or estimateof an angle of arrival, AoA, between a wireless device and a plane of anantenna array of the network node. According to one embodiment of thisaspect, the spatial metric is a measure of spatial channel of a wirelessdevice within a subgroup with respect to the network node.

According to one embodiment of this aspect, the predefined criterion isassociated with a difference of spatial metrics between two wirelessdevices that is greater than a predefined threshold. According to oneembodiment of this aspect, the predefined criterion is associated withan absolute value of an inner product of the normalized spatial metricsof any two wireless devices that is less than a predefined threshold.According to one embodiment of this aspect, the allocated resourcesprovide for multi-user multiple-input multiple-output, MU-MIMO,transmission. According to one embodiment of this aspect, the referencesignal ports corresponds to a rank of the transmission to the firstwireless device.

According to one embodiment of this aspect, a number of physicalresource blocks, PRBs, allocated to the first wireless device aredetermined where the scheduling of the at least one shared referenceport to the first wireless device and second wireless device being basedon the determined number of PRBs. According to one embodiment of thisaspect, the first wireless device is scheduled for a reference signalport combination for one selected from a group consisting of: a onefront-load reference signal symbol configuration; and a two front-loadreference signal symbol configuration. According to one embodiment ofthis aspect, resources for reference signal signaling for a plurality ofwireless devices including the first wireless device are allocated wherethe allocated resources configured to separate, in a slot, at least onetransmission layer of each of the plurality of wireless devices fromeach other, respectively.

According to another aspect of the disclosure, a network node isprovided. The network node includes processing circuitry configured to:allocate resources for demodulation reference signal, DMRS, signalingfor a first wireless device, the allocated resources configured toseparate, in a slot, at least one transmission layer of the firstwireless device from at least one transmission layers of a secondwireless device by at least one of: scheduling the first wireless deviceand second wireless device different DMRS ports that are separated byusing the same resource elements and different code divisionmultiplexing, CDM, codes, the first wireless device and second wirelessdevice having associated scrambling sequences, scheduling the firstwireless device and second wireless device at least one shared DMRS portusing the same resource elements and CDM code, the first wireless deviceand second wireless device having different scrambling sequences,scheduling the first wireless device and second wireless device ondifferent DMRS ports that are separated by frequency divisionmultiplexing, FDM, by using different resource elements and the same CDMcodes, the first and second wireless device having associated scramblingsequences; and scheduling the first wireless device and second wirelessdevice on different DMRS ports that are separated through both FDM andCDM by using different resource elements and different CDM codes, thefirst wireless device and second wireless device having associatedscrambling sequences. The processing circuitry being further configuredto participate in one selected from a group consisting of single-usermultiple-input multiple-output, SU-MIMO, and multi-user-MIMO, MU-MIMO,based at least in part on the allocated resources for DMRS signaling.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete understanding of the present embodiments, and theattendant advantages and features thereof, will be more readilyunderstood by reference to the following detailed description whenconsidered in conjunction with the accompanying drawings wherein:

FIG. 1 is a diagram of a DMRS patterns for single symbol DMRS and doublesymbol DMRS;

FIG. 2 is a diagram of type 1 and type 2 DMRS;

FIG. 3 is a diagram for DMRS ports for type 1 DMRS;

FIG. 4 is a diagram for DMRS ports for type 2 DMRS;

FIG. 5 is a schematic diagram of an exemplary network architectureillustrating a communication system according to the principles in thepresent disclosure;

FIG. 6 is a block diagram of a wireless device and network nodeaccording to some embodiments of the present disclosure;

FIG. 7 is a flow diagram of an exemplary process for a network nodeaccording to some embodiments of the present disclosure;

FIG. 8 is a flow diagram of another exemplary process for a network nodeaccording to some embodiments of the present disclosure;

FIG. 9 is a flow diagram of another exemplary process for a network nodeaccording to some embodiments of the present disclosure;

FIG. 10 is a flow diagram of a DMRS resource allocation processaccording to some embodiments of the present disclosure;

FIG. 11 is a flow diagram of another DMRS resource allocation processaccording to some embodiments of the present disclosure;

FIG. 12 is a diagram of an example DMRS resource allocation according tosome embodiments of the present disclosure;

FIG. 13 is a diagram of another example DMRS resource allocationaccording to some embodiments of the present disclosure; and

FIG. 14 is a flow diagram of an exemplary process for a wireless deviceaccording to some embodiments of the present disclosure.

DETAILED DESCRIPTION

Before describing in detail exemplary embodiments, it is noted that theembodiments reside primarily in combinations of apparatus components andprocessing steps related to reference signal configuration andallocation. Accordingly, components have been represented whereappropriate by conventional symbols in the drawings, showing only thosespecific details that are pertinent to understanding the embodiments soas not to obscure the disclosure with details that will be readilyapparent to those of ordinary skill in the art having the benefit of thedescription herein. Like numbers refer to like elements throughout thedescription.

As used herein, relational terms, such as “first” and “second,” “top”and “bottom,” and the like, may be used solely to distinguish one entityor element from another entity or element without necessarily requiringor implying any physical or logical relationship or order between suchentities or elements. The terminology used herein is for the purpose ofdescribing particular embodiments only and is not intended to belimiting of the concepts described herein. As used herein, the singularforms “a”, “an” and “the” are intended to include the plural forms aswell, unless the context clearly indicates otherwise. It will be furtherunderstood that the terms “comprises,” “comprising,” “includes” and/or“including” when used herein, specify the presence of stated features,integers, steps, operations, elements, and/or components, but do notpreclude the presence or addition of one or more other features,integers, steps, operations, elements, components, and/or groupsthereof.

In embodiments described herein, the joining term, “in communicationwith” and the like, may be used to indicate electrical or datacommunication, which may be accomplished by physical contact, induction,electromagnetic radiation, radio signaling, infrared signaling oroptical signaling, for example. One having ordinary skill in the artwill appreciate that multiple components may interoperate andmodifications and variations are possible of achieving the electricaland data communication.

In some embodiments described herein, the term “coupled,” “connected,”and the like, may be used herein to indicate a connection, although notnecessarily directly, and may include wired and/or wireless connections.

The term “network node” used herein can be any kind of network nodecomprised in a radio network which may further comprise any of basestation (BS), radio base station, base transceiver station (BTS), basestation controller (BSC), radio network controller (RNC), g Node B(gNB), evolved Node B (eNB or eNodeB), Node B, multi-standard radio(MSR) radio node such as MSR BS, multi-cell/multicast coordinationentity (MCE), relay node, donor node controlling relay, radio accesspoint (AP), transmission points, transmission nodes, Remote Radio Unit(RRU) Remote Radio Head (RRH), a core network node (e.g., mobilemanagement entity (MME), self-organizing network (SON) node, acoordinating node, positioning node, MDT node, etc.), an external node(e.g., 3rd party node, a node external to the current network), nodes indistributed antenna system (DAS), a spectrum access system (SAS) node,an element management system (EMS), etc. The network node may alsocomprise test equipment. The term “radio node” used herein may be usedto also denote a wireless device (WD) such as a wireless device (WD) ora radio network node.

In some embodiments, the non-limiting terms wireless device (WD) or auser equipment (UE) are used interchangeably. The WD herein can be anytype of wireless device capable of communicating with a network node oranother WD over radio signals, such as wireless device (WD). The WD mayalso be a radio communication device, target device, device to device(D2D) WD, machine type WD or WD capable of machine to machinecommunication (M2M), low-cost and/or low-complexity WD, a sensorequipped with WD, Tablet, mobile terminals, smart phone, laptop embeddedequipped (LEE), laptop mounted equipment (LME), USB dongles, CustomerPremises Equipment (CPE), an Internet of Things (IoT) device, or aNarrowband IoT (NB-IOT) device etc.

Also, in some embodiments, the generic term “radio network node” isused. It can be any kind of a radio network node which may comprise anyof base station, radio base station, base transceiver station, basestation controller, network controller, RNC, evolved Node B (eNB), NodeB, gNB, Multi-cell/multicast Coordination Entity (MCE), relay node,access point, radio access point, Remote Radio Unit (RRU) Remote RadioHead (RRH).

The term signal used herein can be any physical signal or physicalchannel. Examples of downlink physical signals are reference signal suchas Primary Synchronization Signal (PSS), Secondary SynchronizationSignal (SSS), Cell Specific Reference Signal (CRS), PositioningReference Signal (PRS), Channel State Information Reference Signal(CSI-RS), Demodulation Reference Signal (DMRS), Narrowband ReferenceSignal (NRS), Narrowband Primary Synchronization Signal (NPSS),Narrowband Secondary Synchronization Signal (NSSS), SynchronizationSignals (SS), Multimedia Broadcast Single Frequency Reference Signal(MBSFN RS) etc. Examples of uplink physical signals are reference signalsuch as Sounding Reference Signal (SRS), DMRS, etc. The term physicalchannel (e.g., in the context of channel reception) used herein is alsocalled as ‘channel. The physical channel carries higher layerinformation (e.g. RRC, logical control channel, etc.). Examples ofdownlink physical channels are Physical Broadcast Channel (PBCH),Narrowband Physical Broadcast Channel (NPBCH), Physical Downlink ControlChannel (PDCCH), Physical Downlink Shared Channel (PDSCH), shortPhysical Downlink Shared Channel (sPDSCH), Machine Type Communication(MTC) physical downlink control channel (MPDCCH), Narrowband PhysicalDownlink Control Channel (NPDCCH), Narrow Physical Downlink SharedChannel NPDSCH, Enhanced Physical Downlink Control Channel (E-PDCCH),etc. Examples of uplink physical channels are shorten Physical UplinkControl Channel (sPUCCH). shorten Physical Uplink Shared Channel(sPUSCH), Physical Uplink Shared Channel (PUSCH), Physical UplinkControl Channel (PUCCH), Narrowband Physical Uplink Shared Channel(NPUSCH), Physical Random Access Channel (PRACH), Narrowband PhysicalRandom Access Channel (NPRACH), etc.

The term resource and/or resource element used herein may correspond toany type of physical resource or radio resource expressed in terms oflength of time and/or frequency. Signals are transmitted or received bya radio node over a time resource. Examples of time resources are:symbol, time slot, subframe, radio frame, Transmission Time Interval(TTI), interleaving time, etc.

The term time resource used herein may correspond to any type ofphysical resource or radio resource expressed in terms of length oftime. Examples of time resources are: symbol, time slot, subframe, radioframe, TTI, interleaving time, etc.

An indication generally may explicitly and/or implicitly indicate theinformation it represents and/or indicates. Implicit indication may forexample be based on position and/or resource used for transmission.Explicit indication may for example be based on a parametrization withone or more parameters, and/or one or more index or indices, and/or oneor more bit patterns representing the information. It may in particularbe considered that control signaling as described herein, based on theutilized resource sequence, implicitly indicates the control signalingtype.

A cell may be generally a communication cell, e.g., of a cellular ormobile communication network, provided by a node. A serving cell may bea cell on or via which a network node (the node providing or associatedto the cell, e.g., base station, gNB or eNodeB) transmits and/or maytransmit data (which may be data other than broadcast data) to a userequipment, in particular control and/or user or payload data, and/or viaor on which a user equipment transmits and/or may transmit data to thenode; a serving cell may be a cell for or on which the user equipment isconfigured and/or to which it is synchronized and/or has performed anaccess procedure, e.g., a random access procedure, and/or in relation towhich it is in a RRC_connected or RRC_idle state, e.g., in case the nodeand/or user equipment and/or network follow the LTE-standard. One ormore carriers (e.g., uplink and/or downlink carrier/s and/or a carrierfor both uplink and downlink) may be associated with a cell.

Configuring a terminal or wireless device or node may involveinstructing and/or causing the wireless device or node to change itsconfiguration, e.g., at least one setting and/or register entry and/oroperational mode. A terminal or wireless device or node may be adaptedto configure itself, e.g., according to information or data in a memoryof the terminal or wireless device. Configuring a node or terminal orwireless device by another device or node or a network may refer toand/or comprise transmitting information and/or data and/or instructionsto the wireless device or node by the other device or node or thenetwork, e.g., allocation data (which may also be and/or compriseconfiguration data) and/or scheduling data and/or scheduling grants.Configuring a terminal may include sending allocation/configuration datato the terminal indicating which modulation and/or encoding to use. Aterminal may be configured with and/or for scheduling data and/or touse, e.g., for transmission, scheduled and/or allocated uplinkresources, and/or, e.g., for reception, scheduled and/or allocateddownlink resources. Uplink resources and/or downlink resources may bescheduled and/or provided with allocation or configuration data.

Generally, configuring may include determining configuration datarepresenting the configuration and providing, e.g. transmitting, it toone or more other nodes (parallel and/or sequentially), which maytransmit it further to the radio node (or another node, which may berepeated until it reaches the wireless device). Alternatively, oradditionally, configuring a radio node, e.g., by a network node or otherdevice, may include receiving configuration data and/or data pertainingto configuration data, e.g., from another node like a network node,which may be a higher-level node of the network, and/or transmittingreceived configuration data to the radio node. Accordingly, determininga configuration and transmitting the configuration data to the radionode may be performed by different network nodes or entities, which maybe able to communicate via a suitable interface, e.g., an X2 interfacein the case of LTE or a corresponding interface for NR. Configuring aterminal (e.g. wireless device) may comprise scheduling downlink and/oruplink transmissions for the terminal, e.g. downlink data and/ordownlink control signaling and/or DCI and/or uplink control or data orcommunication signaling, in particular acknowledgement signaling, and/orconfiguring resources and/or a resource pool therefor. In particular,configuring a terminal (e.g. wireless device) may comprise configuringthe wireless device to perform certain measurements on certain subframesor radio resources and reporting such measurements according toembodiments of the present disclosure.

Data may refer to any kind of data, in particular, any one of and/or anycombination of control data or user data or payload data. Controlinformation (which may also be referred to as control data) may refer todata controlling and/or scheduling and/or pertaining to the process ofdata transmission and/or the network or terminal operation.

It may be considered for cellular communication there is provided atleast one uplink (UL) connection and/or channel and/or carrier and atleast one downlink (DL) connection and/or channel and/or carrier, e.g.,via and/or defining a cell, which may be provided by a network node, inparticular, a base station, gNB or eNodeB. An uplink direction may referto a data transfer direction from a terminal to a network node, e.g.,base station, gNB and/or relay station. A downlink direction may referto a data transfer direction from a network node, e.g., base station,gNB and/or relay node, to a terminal. UL and DL may be associated todifferent frequency resources, e.g., carriers and/or spectral bands. Acell may comprise at least one uplink carrier and at least one downlinkcarrier, which may have different frequency bands. A network node, e.g.,a base station, gNB or eNodeB, may be adapted to provide and/or defineand/or control one or more cells.

Note that although terminology from one particular wireless system, suchas, for example, 3GPP LTE and/or New Radio (NR), may be used in thisdisclosure, this should not be seen as limiting the scope of thedisclosure to only the aforementioned system. Other wireless systems,including without limitation Wide Band Code Division Multiple Access(WCDMA), Worldwide Interoperability for Microwave Access (WiMax), UltraMobile Broadband (UMB) and Global System for Mobile Communications(GSM), may also benefit from exploiting the ideas covered within thisdisclosure.

Note further, that functions described herein as being performed by awireless device or a network node may be distributed over a plurality ofwireless devices and/or network nodes. In other words, it iscontemplated that the functions of the network node and wireless devicedescribed herein are not limited to performance by a single physicaldevice and, in fact, can be distributed among several physical devices.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which this disclosure belongs. It willbe further understood that terms used herein should be interpreted ashaving a meaning that is consistent with their meaning in the context ofthis specification and the relevant art and will not be interpreted inan idealized or overly formal sense unless expressly so defined herein.

Referring again to the drawing figures, in which like elements arereferred to by like reference numerals, there is shown in FIG. 5 aschematic diagram of a communication system 10, according to anembodiment, such as a 3GPP-type cellular network that may supportstandards such as LTE and/or NR (5G), which includes an access network12, such as a radio access network, and a core network 14. The accessnetwork 12 comprises a plurality of network nodes 16 a, 16 b, 16 c(referred to collectively as network nodes 16), such as NBs, eNBs, gNBsor other types of wireless access points, each defining a correspondingcoverage area 18 a, 18 b, 18 c (referred to collectively as coverageareas 18). Each network node 16 a, 16 b, 16 c is connectable to the corenetwork 14 over a wired or wireless connection 20. A first wirelessdevice (WD) 22 a located in coverage area 18 a is configured towirelessly connect to, or be paged by, the corresponding network node 16c. A second WD 22 b in coverage area 18 b is wirelessly connectable tothe corresponding network node 16 a. While a plurality of WDs 22 a, 22 b(collectively referred to as wireless devices 22) are illustrated inthis example, the disclosed embodiments are equally applicable to asituation where a sole WD is in the coverage area or where a sole WD isconnecting to the corresponding network node 16. Note that although onlytwo WDs 22 and three network nodes 16 are shown for convenience, thecommunication system may include many more WDs 22 and network nodes 16.

Also, it is contemplated that a WD 22 can be in simultaneouscommunication and/or configured to separately communicate with more thanone network node 16 and more than one type of network node 16. Forexample, a WD 22 can have dual connectivity with a network node 16 thatsupports LTE and the same or a different network node 16 that supportsNR. As an example, WD 22 can be in communication with an eNB forLTE/E-UTRAN and a gNB for NR/NG-RAN.

A network node 16 is configured to include allocation unit 24 forperforming one or more network node 16 functions described herein. Awireless device 22 is configured to include a reference signal (RS) unit26 for performing one or more wireless device 22 functions describedherein.

Example implementations, in accordance with an embodiment, of the WD 22and network node 16 discussed in the preceding paragraphs will now bedescribed with reference to FIG. 6. The communication system 10 includesa network node 16 provided in a communication system 10 and includinghardware 28 enabling it to communicate with one or more other networknodes 16 and/or with the WD 22. The hardware 28 may include acommunication interface 30 for setting up and maintaining a wired orwireless connection with an interface of a different communicationdevice of the communication system 10, as well as a radio interface 32for setting up and maintaining at least a wireless connection 34 with aWD 22 located in a coverage area 18 served by the network node 16. Theradio interface 32 may be formed as or may include, for example, one ormore RF transmitters, one or more RF receivers, and/or one or more RFtransceivers.

In the embodiment shown, the hardware 28 of the network node 16 furtherincludes processing circuitry 36. The processing circuitry 36 mayinclude a processor 38 and a memory 40. In particular, in addition to orinstead of a processor, such as a central processing unit, and memory,the processing circuitry 36 may comprise integrated circuitry forprocessing and/or control, e.g., one or more processors and/or processorcores and/or FPGAs (Field Programmable Gate Array) and/or ASICs(Application Specific Integrated Circuitry) adapted to executeinstructions. The processor 38 may be configured to access (e.g., writeto and/or read from) the memory 40, which may comprise any kind ofvolatile and/or nonvolatile memory, e.g., cache and/or buffer memoryand/or RAM (Random Access Memory) and/or ROM (Read-Only Memory) and/oroptical memory and/or EPROM (Erasable Programmable Read-Only Memory).

Thus, the network node 16 further has software 42 stored internally in,for example, memory 40, or stored in external memory (e.g., database,storage array, network storage device, etc.) accessible by the networknode 16 via an external connection. The software 42 may be executable bythe processing circuitry 36. The processing circuitry 36 may beconfigured to control any of the methods and/or processes describedherein and/or to cause such methods, and/or processes to be performed,e.g., by network node 16. Processor 38 corresponds to one or moreprocessors 38 for performing network node 16 functions described herein.The memory 40 is configured to store data, programmatic software codeand/or other information described herein. In some embodiments, thesoftware 42 may include instructions that, when executed by theprocessor 38 and/or processing circuitry 36, causes the processor 38and/or processing circuitry 36 to perform the processes described hereinwith respect to network node 16. For example, processing circuitry 36 ofthe network node 16 may include allocation unit 24 configured toallocate resources as described herein.

The communication system 10 further includes the WD 22 already referredto. The WD 22 may have hardware 43 that may include a radio interface 44configured to set up and maintain a wireless connection 34 with anetwork node 16 serving a coverage area 18 in which the WD 22 iscurrently located. The radio interface 44 may be formed as or mayinclude, for example, one or more RF transmitters, one or more RFreceivers, and/or one or more RF transceivers.

The hardware 43 of the WD 22 further includes processing circuitry 46.The processing circuitry 46 may include a processor 48 and memory 50. Inparticular, in addition to or instead of a processor, such as a centralprocessing unit, and memory, the processing circuitry 46 may compriseintegrated circuitry for processing and/or control, e.g., one or moreprocessors and/or processor cores and/or FPGAs (Field Programmable GateArray) and/or ASICs (Application Specific Integrated Circuitry) adaptedto execute instructions. The processor 48 may be configured to access(e.g., write to and/or read from) memory 50, which may comprise any kindof volatile and/or nonvolatile memory, e.g., cache and/or buffer memoryand/or RAM (Random Access Memory) and/or ROM (Read-Only Memory) and/oroptical memory and/or EPROM (Erasable Programmable Read-Only Memory).

Thus, the WD 22 may further comprise software 52, which is stored in,for example, memory 50 at the WD 22, or stored in external memory (e.g.,database, storage array, network storage device, etc.) accessible by theWD 22. The software 52 may be executable by the processing circuitry 46.The software 52 may include a client application 54. The clientapplication 54 may be configured to provide a service to a human ornon-human user via the WD 22. The client application 54 may interactwith the user to generate the user data that it provides.

The processing circuitry 46 may be configured to control any of themethods and/or processes described herein and/or to cause such methods,and/or processes to be performed, e.g., by WD 22. The processor 48corresponds to one or more processors 48 for performing WD 22 functionsdescribed herein. The WD 22 includes memory 50 that is configured tostore data, programmatic software code and/or other informationdescribed herein. In some embodiments, the software 52 and/or the clientapplication 54 may include instructions that, when executed by theprocessor 48 and/or processing circuitry 46, causes the processor 48and/or processing circuitry 46 to perform the processes described hereinwith respect to WD 22. For example, the processing circuitry 46 of thewireless device 22 may include a reference signal (RS) unit 26configured to transmit and/or received a reference signal on allocatedresources as described herein.

In some embodiments, the inner workings of the network node 16 and WD 22may be as shown in FIG. 6 and independently, the surrounding networktopology may be that of FIG. 5.

Although FIGS. 5 and 6 show various “units” such as RS unit 26 andallocation unit 24 as being within a respective processor, it iscontemplated that these units may be implemented such that a portion ofthe unit is stored in a corresponding memory within the processingcircuitry. In other words, the units may be implemented in hardware orin a combination of hardware and software within the processingcircuitry.

FIG. 7 is a flowchart of an exemplary process in a network node 16according to one or more embodiments of the disclosure. One or moreBlocks and/or functions performed by network node 16 may be performed byone or more elements of network node 16 such as by allocation unit 24 inprocessing circuitry 36, processor 38, radio interface 32, etc. In oneor more embodiments, network node 16 such as via one or more ofprocessing circuitry 36, processor 38 and radio interface 32 isconfigured to allocate (Block S100) resources for a reference signalsignaling for a first wireless device where the allocated resources areconfigured to separate, in a slot, at least one transmission layer ofthe first wireless device from at least one transmission layer of asecond wireless device by at least one of: scheduling the first wirelessdevice and second wireless device different reference signal ports thatare separated by using the same resource elements and different codedivision multiplexing, CDM, codes, the first wireless device and secondwireless device having associated scrambling sequences, scheduling thefirst wireless device and second wireless device at least one sharedreference signal port using the same resource elements and CDM code, thefirst wireless device and second wireless device having differentscrambling sequences, scheduling the first wireless device and secondwireless device on different reference signal ports that are separatedby frequency division multiplexing, FDM, by using different resourceelements and the same CDM codes, the first and second wireless devicehaving associated scrambling sequences, and scheduling the firstwireless device and second wireless device on different reference signalports that are separated through both FDM and CDM by using differentresource elements and different CDM codes, the first wireless device andsecond wireless device having associated scrambling sequences.

In one or more embodiments, the first wireless device and the secondwireless device having the at least one shared reference signal port arepart of a wireless device sub-group, the wireless device sub-groupmeeting at least one predefined spatial condition. In one or moreembodiments, the allocated resources provide for Multi-User,MU-Multiple-Input Multiple-Output, MIMO, transmission. In one or moreembodiments, the reference signal ports are separated by frequencydivision multiplexing. In one or more embodiments, the number ofscheduling reference signal ports correspond to the rank of thetransmission of the first wireless device.

In one or more embodiments, the processing circuitry is furtherconfigured to determine a number of physical resource blocks, PRBs,allocated to the first wireless device, the scheduling of the at leastone shared reference port to the first wireless device and secondwireless device being based on the determined number of PRBs. In one ormore embodiments, the first wireless device is scheduled for a referencesignal port combination for a one front-load reference signal symbolconfiguration. In one or more embodiments, the first wireless device isscheduled for a reference signal port combination for a two front-loadreference signal symbol configuration. In one or more embodiments, theprocessing circuitry is further configured to: allocate resources forreference signal signaling for a plurality of wireless devices, theallocated resources configured to separate, in a slot, at least onetransmission layer of each of the plurality of wireless devices fromeach other, respectively, by at least one of: scheduling at least twowireless devices different reference signal ports, the at least twowireless devices having the same scrambling identifier; and schedulingat least two other wireless devices at least one shared reference signalport, the at least two other wireless devices having differentscrambling identifiers. In one or more embodiments, the separation ofports is spatial separation.

Having generally described embodiments and process flow for referencesignal configuration and allocation in accordance with the principles ofthe present disclosure, details relating to the reference signal (e.g.,DL DMRS) configuration and allocation to one or more wireless devices 22will now be described.

Configuration

For DL DMRS configuration, the following RRC parameters may be used:

-   -   dmrs-Type. Type 1 may be beneficial for high frequency selective        channels while type 2 may be configured if more than 8 MU-MIMO        layers may need to be supported.    -   dmrs-AdditionalPosition. More additional DMRS can give a better        channel estimation with large Doppler spread. However, more        additional DMRS may result in more overhead.    -   maxLength. The maximum number of OFDM symbols for DL front        loaded DMRS. To support more than 6 MU-MIMO layers, length of 2        may be configured.    -   scramblingID0 and scramblingID1. The DL DMRS scrambling        initialization that are used to initialize the scrambling        sequences. In one or more embodiments, the algorithm to        determine the two IDs is described below:

In some embodiments, there are 65536 valid values for scrambling IDs.The values may be divided into M groups. All of the groups may or maynot have an equal number of values. One group of values may be assignedto a cell, either randomly or based on certain rules. For a given cell,one value from the group is selected and configured as scramblingID0 forall wireless devices 22 in the cell. For a particular wireless device 22in the cell, one value from the remaining IDs (without the selected IDfor scramblingID0) may be selected and configured as scramblingID1 forthe wireless device 22. The selection can be random or based on aRound-Robin pattern. In other embodiments, two distinct values areselected randomly from a group and are configured as scramblingID0 andscramblingID1 for a wireless device 22.

Allocation

For DL DMRS allocation, the antenna port field in DCI can dynamicallycontrol the DL DMRS allocation. In one or more embodiments, only certainDMRS port combinations may be allowed for 3GPP networks. Those portcombinations are referred to as allowed DMRS port combinations.

For SU-MIMO Transmissions:

In one or more embodiments, the configured scramblingID0 may be used.With a wireless device 22 rank, an attempt is made to find the allowedDMRS port combinations that match the rank for the given DMRSconfiguration. If there are multiple allowed DMRS port combinations thatmatch the rank, there are various options for assigning a portcombination. In one or more embodiments, any port combination can beselected for the wireless device 22. In one or more other embodiments,the port combination that has a maximum number of ports separatedthrough FDM is selected. For example, type 1 single-symbol based DMRS isconfigured for a wireless device 22 and two CDM groups are used forDMRS. If the wireless device 22's rank is 2, there are several allowedport combinations with two ports, such as (0, 1), (2, 3), and (0, 2).Since port 0 and 2 are separated by FDM, this FDM based spatialseparation can lead to better channel estimation; therefore, networknode 16 selects the port combination (0, 2) for the wireless device 22.

For MU-MIMO Transmissions:

For MU-MIMO transmissions for a group of co-scheduled wireless devices22, the allocation of scrambling ID and DMRS port may be as follows:

Assumptions: All wireless devices 22 in a cell are configured with thesame dmrs-Type, dmrs-AdditionalPosition and maxLength.

Algorithm:

Some 3GPP allowed port combinations may not be considered for MU-MIMOsince these allowed port combinations fragment the port space. Forexample, in cases of type 1, double-symbol based DMRS, port combination(0, 2, 4, 6) (note that these ports may correspond to port 1000, 1002,1004 and 1006 in 3GPP specifications but to simplify notation the portsare referred to as port 0, 1, 2 and 6, respectively) may not be good andmay fragment the port space. If this port combination is assigned to awireless device 22, no port combination can be found for anotherwireless device 22 with rank of 2 due to the port space fragmentation.The reduced 3GPP allowed port combinations (i.e., subset of 3GPP allowedport combinations that may not fragment the port space) are referred toherein as MU-MIMO port combinations.

For a given configured dmrs-Type, dmrs-AdditionalPosition and maxLength,let N_FDM denote the max number of DMRS ports that are separated throughFDM, and N_MAX denotes the max number of DMRS ports supported for thegiven configuration. If maxLength is set to 2, N_MAX1 denotes the maxnumber of DMRS ports with single-symbol based DMRS, and N_MAX2 denotesthe max number of DMRS ports with double-symbol based DMRS.

Two wireless devices 22 may be considered to be “spatially separated” ifone of the following conditions or predefined criterion is/are met:

-   -   If the difference between the angle of arrival (AoA) of the two        wireless devices 22 is greater than a threshold where the AoA is        one example of a spatial metric.    -   If the orthogonal factor between DL channels of the two wireless        devices 22 is smaller than a threshold. Assuming H_(i) ^(n) is        the DL channel vector for i-th receive antenna of wireless        device n, and H_(j) ^(m) is the DL channel vector for j-th        receive antenna of wireless device m, the orthogonal factor is        defined as

$\frac{\left\langle {H_{i}^{n},H_{j}^{m}} \right\rangle}{{H_{i}^{n}}^{2}{H_{j}^{m}}^{2}}$

where

H_(i) ^(n), H_(h) ^(m)

represents the inner product of the two channel vectors, and ∥A∥ is theEuclidean distance of the vector A. Alternatively the orthogonalityfactor can also be defined as

$\frac{E\left\lbrack \left\langle {H_{i}^{n},H_{j}^{m}} \right\rangle \right\rbrack}{{E\left\lbrack {H_{i}^{n}}^{2} \right\rbrack}{E\left\lbrack {H_{j}^{m}}^{2} \right\rbrack}}$

where E[ ] is the expectation operator. In one or more embodiments, theorthogonal factor is a measure of channel separation of two wirelessdevices 22 within a subgroup with respect to the network node 16. The DLchannel vector or orthogonal factor is an example of a spatial metric.

-   -   Both AoA or orthogonal factor can be measured based on the UL        reception from the wireless device 22. For example, the channel        can be estimated from one of the UL reference signals and        further compute AoA or orthogonality factor. For improving the        estimation accuracy, the measurements can be filtered over time.        In one or more embodiments, the predefined criterion is        associated with a difference of spatial metrics between two        wireless devices that is greater than a predefined threshold. In        one or more embodiments, the predefined criterion is associated        with an absolute value of an inner product of normalized spatial        metrics of any two wireless devices 22 that is less than a        predefined threshold. A wireless device 22 can be spatially        separated from multiple other wireless devices 22.

Assuming that a scheduler, such as a scheduler of the network node 16,has decided to co-schedule N wireless devices 22 for PDSCH transmissionsin a TTI (the same frequency/time resources are shared by those wirelessdevices 22). Those wireless devices 22 are mutually spatially separated.These mutually spatially separated wireless devices 22 may be referredto as a MU-MIMO wireless device group. Among the N wireless devices 22,there are wireless devices 22 that meet a more stringent spatialseparation requirement (e.g., such as wireless devices 22 being assignedports separated by FDM). If two wireless device 22 meet the stringentspatial separation requirement, the two wireless devices 22 arespatially well separated or spatially separated more than just beingmutually spatially separated.

In one or more embodiments, scheduling spatially separated wirelessdevices 22 corresponds to allocating resources configured to separate,in a slot, at least one transmission layer of a first wireless device 22from at least one transmission layer of a second wireless device 22 byscheduling the first wireless device 22 and second wireless device 22 ondifferent reference signal ports (e.g., DMRS ports) that are separatedby using the same resource elements and different CDM codes (e.g.,orthogonal codes) where the first wireless device 22 and second wirelessdevice 22 have associated scrambling sequences, as described herein.

In one or more embodiments, scheduling spatially separated wirelessdevices 22 corresponds to allocating resources configured to separate,in a slot, at least one transmission layer of a first wireless device 22from at least one transmission layer of a second wireless device 22 byscheduling the first wireless device 22 and second wireless device 22 onat least one shared reference signal port using the same resourceelements and CDM code where the first wireless device 22 and secondwireless device 22 having different scrambling sequences.

In one or more embodiments, scheduling spatially separated wirelessdevices 22 corresponds to allocating resources configured to separate,in a slot, at least one transmission layer of a first wireless device 22from at least one transmission layer of a second wireless device 22 byscheduling the first wireless device 22 and second wireless device 22 ondifferent reference signal ports that are separated by FDM usingdifferent resource elements and the same CDM codes where the firstwireless device 22 and second wireless device 22 have associatedscrambling sequences.

In one or more embodiments, scheduling spatially separated wirelessdevices 22 corresponds to allocating resources configured to separate,in a slot, at least one transmission layer of a first wireless device 22from at least one transmission layer of a second wireless device 22 byscheduling the first wireless device 22 and second wireless device 22 ondifferent reference signal ports that are separated through both FDM andCDM by using different resource elements and different CDM codes wherethe first wireless device 22 and second wireless device 22 havingassociated scrambling sequence.

Within a MU-MIMO wireless device group, one can form multiple wirelessdevices 22 sub-groups. The wireless devices 22 in each sub-group aremutually well separated. In one or more embodiments, one wireless device22 is in multiple sub-groups.

Define the accumulated rank, R=Σ_(i=1) ^(N)R_(i), where R_(i) is therank for i-th wireless device 22.

Example Process/Algorithm for Case 1: N_(MAX1)≥R

  Sort N wireless devices 22 based scheduling priority,   and set thenumber of available DMRS ports, N_(avail), to N_(MAX1)   Limit theMU-MIMO port combinations to those   with 1 front-load DMRS symbol  While N_(avail) > 0 and there are un-processed wireless devices 22    Select the wireless device 22 with the highest scheduling priorityamong the un-processed wireless devices 22     Select a MU-MIMO portcombination that contains     only unassigned ports and matches wirelessdevice 22's rank, starting from the highest possible port number     Ifsuch a port combination cannot be found       select a MU-MIMO portcombination with       a maximum number of unassigned ports       If thedifference between wireless devices 22's rank and the number of ports inthe port combination is greater than a threshold         Do not schedulethe wireless device 22         Mark the wireless device 22 as dropped      Else         Schedule the wireless device 22 with reduced rank        Mark the wireless device 22 as processed         Indicatescrambling ID0 in DCI       End if     Else        Schedule the wirelessdevice 22 with its rank        Mark the wireless device 22 as processed       Indicate scrambling ID0 in DCI        End if       UpdateN_(avail) End while

If there are still unprocessed wireless devices 22 or dropped wirelessdevices 22, the algorithm can be executed again with N_(avail) beinginitialized to N_(MAX2). In one or more embodiments, the MU-MIMO portcombinations may be limited to those with 2 front-load DMRS symbol.

Example Process/Algorithm for Case 2: R>N_(MAX1):

  Sort N wireless devices 22 based scheduling priority, and   set thenumber of available DMRS ports, N_(avail), to N_(MAX2)   Limit theMU-MIMO port combinations to those   with 2 front-load DMRS symbol  While N_(avail) > 0 and there are un-processed wireless devices 22    Select the wireless device 22 with the highest scheduling priorityamong the un-processed wireless devices 22     Select a MU-MIMO portcombination that contains     only unassigned ports and matches wirelessdevice 22's rank, starting from the highest possible port number     Ifsuch a port combination cannot be found       select a MU-MIMO portcombination with a maximum       number of unassigned ports       If thedifference between wireless device 22's rank and the number of ports inthe port combination is greater than a threshold         Do not schedulethe wireless device 22         Mark the wireless device 22 as DMRSresource not assigned dropped       Else         Schedule the wirelessdevice 22 with reduced rank         Mark the wireless device 22 asprocessed         Indicate scrambling ID0 in DCI       End if       Else        Schedule the wireless device 22 with it rank         Mark thewireless device 22 as processed         Indicate scrambling ID0 in DCI      End if       Update N_(avail) End whileWhile there are un-processed wireless devices 22 or wireless devices 22that do not have a DMRS resource assigned

Select the wireless device 22 with the highest scheduling priority amongthe un-processed wireless devices 22

Identify the wireless devices 22 that are not in any wireless device 22sub-groups that contains this wireless device 22

Generate a list of ports that are not assigned to wireless device 22identified above (the same list can be generated as the ports assignedto all other wireless devices 22 that are in any sub-group containingthis wireless device 22 plus the ports that are not assigned to anywireless device 22)

If a port identified in the previous step are already shared by acertain number of wireless devices 22, remove the port from the list.The final list contains all ports this wireless device 22 can share withother wireless devices 22 when different scrambling sequences are used

Among the ports obtained in the previous step, identify all MU-MIMO portcombinations for which the difference between the wireless device 22'srank and the number of ports for the MU-MIMO port combination is notgreater than a threshold

Sort the MU-MIMO port combinations based on the difference between thewireless device 22's rank and the number of ports for the MU-MIMO portcombination. The first MU-MIMO port combination has the least difference

For each port combination

-   -   If, according to one of the configured scrambling ID, the        scrambling sequence of the selected wireless device 22 for any        port within the port combination is different from the        scrambling sequence of any other wireless device 22 that uses        the same port

     Use the configured scrambling ID in DCI for the wireless device 22     Select the port combination for the wireless device 22      End thefor loop    End if  End for  Mark the wireless device 22 as processedEnd while

FIG. 8 is a flowchart of an exemplary process for allocating DMRS portsaccording to some embodiments of the disclosure. One or more Blocksand/or functions performed by network node 16 may be performed by one ormore elements of network node 16 such as by allocation unit 24 inprocessing circuitry 36, processor 38, radio interface 32, etc. In oneor more embodiments, network node 16 such as via one or more ofprocessing circuitry 36, processor 38 and radio interface 32 isconfigured to configure (Block S102) DMRS scrambling IDs for one or morewireless devices 22, as described herein. In one or more embodiments,network node 16 such as via one or more of processing circuitry 36,processor 38 and radio interface 32 is configured to form (Block S104)wireless device 22 sub-groups with a predefined spatial separation amongthe wireless devices 22, as described herein. In one or moreembodiments, network node 16 such as via one or more of processingcircuitry 36, processor 38 and radio interface 32 is configured to, whenDMRS ports (i.e., type of reference signal port) are available, assign(Block S106) an allowed set of DMRS ports with scrambling ID-0 towireless devices 22 in the order of wireless device 22 priority based onthe required number of layer(s) for each wireless device 22, asdescribed herein.

In one or more embodiments, network node 16 such as via one or more ofprocessing circuitry 36, processor 38 and radio interface 32 isconfigured to, when DMRS ports are exhausted, assign (Block S108) anallowed set of DMRS ports from DMRS ports already assigned to otherwireless devices 22 within a wireless device 22 sub-group, as describedherein. In one or more embodiments, network node 16 such as via one ormore of processing circuitry 36, processor 38 and radio interface 32 isconfigured to repeat one or more of Blocks S102-S108 (Block S110) untilall of the wireless devices 22 are assigned with DMRS ports or until allthe DMRS ports are exhausted and port sharing has been exhausted, asdescribed herein.

FIG. 9 is a flowchart of an exemplary process for allocated DMRS portsas described herein such as with respect to Case 2: R>N_(MAX1). In oneor more embodiments, network node 16 such as via one or more ofprocessing circuitry 36, processor 38 and radio interface 32 isconfigured to determine (Block S112) a MU-MIMO wireless device group{U_(k), k=0, . . . , N−1}. In one or more embodiments, network node 16such as via one or more of processing circuitry 36, processor 38 andradio interface 32 is configured to set (Block S114) N_(L)=N_(max) and

=0.

In one or more embodiments, network node 16 such as via one or more ofprocessing circuitry 36, processor 38 and radio interface 32 isconfigured to determine (Block S116) whether N_(L)>0. If N_(L)>0,perform (Block S118) DMRS resource allocation A that is described indetail with respect to FIG. 10. In one or more embodiments, network node16 such as via one or more of processing circuitry 36, processor 38 andradio interface 32 is configured to determine (Block S120) whether

>N. If

is not greater than N, Block S116 may be performed. If

is greater than N, the process may end.

Referring back to Block S116, if N_(L) is not greater than 0, in one ormore embodiments, network node 16 such as via one or more of processingcircuitry 36, processor 38 and radio interface 32 is configured toperform (Block S122) DMRS resource allocation B as described withrespect to FIG. 11. In one or more embodiments, network node 16 such asvia one or more of processing circuitry 36, processor 38 and radiointerface 32 is configured to determine (Block S124) whether

>N. If

is not greater than N, Block S116 may be performed. If

is greater than N, the process may end.

FIG. 10 is a flow diagram of the DMRS resource allocation A process ofBlock S118 according to some embodiments of the disclosure. In one ormore embodiments, network node 16 such as via one or more of processingcircuitry 36, processor 38 and radio interface 32 is configured toselect (Block S126) wireless device k. In one or more embodiments,network node 16 such as via one or more of processing circuitry 36,processor 38 and radio interface 32 is configured to select (Block S128)a MU-MIMO port combination with N_(k) ports. In one or more embodiments,network node 16 such as via one or more of processing circuitry 36,processor 38 and radio interface 32 is configured to determine (BlockS130) whether R_(k)−N_(k)>T1. If R_(k)−N_(k) is greater than T1, in oneor more embodiments, network node 16 such as via one or more ofprocessing circuitry 36, processor 38 and radio interface 32 isconfigured to not schedule (Block S132) the wireless device k.

If R_(k)−N_(k) is not greater than T1, in one or more embodiments,network node 16 such as via one or more of processing circuitry 36,processor 38 and radio interface 32 is configured to schedule (BlockS134) the wireless device k with rank of N_(k). In one or moreembodiments, network node 16 such as via one or more of processingcircuitry 36, processor 38 and radio interface 32 is configured to set(Block S136)

=

+1. In one or more embodiments, network node 16 such as via one or moreof processing circuitry 36, processor 38 and radio interface 32 isconfigured to set (Block S138) N_(L)=N_(L)−N_(k).

FIG. 11 is a flow diagram of the DMRS resource allocation B process ofBlock S122 according to some embodiments of the disclosure. In one ormore embodiments, network node 16 such as via one or more of processingcircuitry 36, processor 38 and radio interface 32 is configured toselect (Block S140) wireless device k. In one or more embodiments,network node 16 such as via one or more of processing circuitry 36,processor 38 and radio interface 32 is configured to identify (BlockS142) the wireless devices that are not in any wireless devicesub-groups containing the wireless device k. In one or more embodiments,network node 16 such as via one or more of processing circuitry 36,processor 38 and radio interface 32 is configured to generate (BlockS144) a list of ports that can be potentially assigned to the wirelessdevice. In one or more embodiments, network node 16 such as via one ormore of processing circuitry 36, processor 38 and radio interface 32 isconfigured to remove (Block S146) the ports that are shared by at leasta predefined number of wireless devices.

In one or more embodiments, network node 16 such as via one or more ofprocessing circuitry 36, processor 38 and radio interface 32 isconfigured to identify (Block S148) all MU-MIMO port combinations thatcan be potentially assigned to the wireless device. In one or moreembodiments, network node 16 such as via one or more of processingcircuitry 36, processor 38 and radio interface 32 is configured to sort(Block S150) all of the MU-MIMO port combinations. In one or moreembodiments, network node 16 such as via one or more of processingcircuitry 36, processor 38 and radio interface 32 is configured todetermine (Block S152) whether all port combinations have been examined.If all port combinations, i.e., MU-MIMO port combinations, have beenexamined, in one or more embodiments, network node 16 such as via one ormore of processing circuitry 36, processor 38 and radio interface 32 isconfigured to mark (Block S154) the wireless device as processed. In oneor more embodiments, network node 16 such as via one or more ofprocessing circuitry 36, processor 38 and radio interface 32 isconfigured to set (Block S156)

=

+1.

If all port combinations have not been examined, in one or moreembodiments, network node 16 such as via one or more of processingcircuitry 36, processor 38 and radio interface 32 is configured toselect (Block S158) the next unexamined port combination. In one or moreembodiments, network node 16 such as via one or more of processingcircuitry 36, processor 38 and radio interface 32 is configured todetermine (Block S160) whether, for a configured scrambling ID, thescrambling sequence for any port within the port combination isdifferent from the scrambling sequence of any other wireless device(s)22 that use the same port. If the scrambling sequence for any port isnot different, Block S152 may be performed. If the scrambling sequencesfor all ports within the port combination are different for a configuredscrambling ID, in one or more embodiments, network node 16 such as viaone or more of processing circuitry 36, processor 38 and radio interface32 is configured to select (Block S162) the scrambling ID. In anotherembodiment, the scrambling sequences for different wireless devices 22can be selected such that their correlation is less than a certain orpredefined threshold. In one or more embodiments, network node 16 suchas via one or more of processing circuitry 36, processor 38 and radiointerface 32 is configured to assign (Block S164) a port combination,i.e., MU-MIMO port combination, and move to Block S154.

The example below is one example of the implementation of the algorithmfor case 2 at network node 16.

Six wireless devices 22 (WD 22(0) to WD 22(5)) are scheduled forMU-MIMO, or the six wireless devices 22 are in a MU-MIMO WD group. Thereare only 8 DMRS ports (port 0 to 7) available for the given DMRSconfiguration.

There are two wireless device sub-groups:

(WD 22(2), WD 22(5))

(WD 22(3), WD 22(4), WD 22(5))

The DMRS resource allocation follows the order of WD priority, from WD22(0) to WD 22(5).

WD 22(0), WD 22(1), and WD 22(2) all have a rank of 2 and are assignedwith ports (6, 7), (4, 5), and (2, 3), respectively.

WD 22(3) has a rank of 1 and is assigned with port 0.

WD 22(4) has a rank of 2, but there is only one port available. WD 22(4)is examined to see if it can share the same ports with other WDs 22.Since WD 22(4) is in only one WD sub-group, which does not contain WD22(0), WD 22(1) and WD 22(2), the ports that can be used by WD 22(4) arethe ports that are not assigned to WD 22(0), WD 22(1) and WD 22(2). Inother words, ports 0 and 1 can be used by WD 22(4). Assuming with one ofthe configured scrambling IDs for WD 22(4), the scrambling sequence forports 0 and 1 for WD 22(4) is different from the scrambling sequenceused by WD 22(3), that ID is used for DCI for WD 22(4) and ports 0 and 1are assigned to WD 22(4).

WD 22(5) has a rank of 2, and it is also be examined to determine if WD22(5) can share the same ports with other WDs 22. WD 22(5) is in two WDsub-groups. The WDs 22 that are not included in either WD sub-group areWD 22(0) and WD 22(1). So, the ports that can be used by WD 22(5) arethe ports that are not assigned to WD 22(0) and WD 22(1), which areports 0 to 3.

For rank 2, the MU-MIMO port combinations that can be used for WD 22(5)are (0, 1) and (2, 3). Port combination (0, 1) can be assigned to WD22(5) if its scrambling sequence is different from the scramblingsequences used by both WD 22(3) and WD 22(4). The final DMRS resourceallocation in this case is shown in FIG. 12 where port X is designatedas PX. Port combination (2, 3) can be assigned to WD 22(5) if itsscrambling sequence is different from the scrambling sequence used by WD22(2). The final DMRS resource allocation in this case is shown in FIG.13 where boxes with the same hatching represent common ports shared byone or more WDs 22. In FIG. 13, the scrambling sequence for WD 22(5) isshown to be z (i.e., scrambling sequence z), which is different from thescrambling sequence y used by WD 22(4). However, this is not required.The scrambling sequence for WD 22(5) may only need to be different fromthat used by WD 22(2). If the maximum number of WDs 22 that share thesame DMRS ports is limited to 2, only port combination (2, 3) can beassigned to WD 22(5).

According to an alternative embodiment, the number of PRBs allocated toa WD 22 is used to determine whether the WD 22 can share a DMRS portwith other WDs 22. The limit of the number of PRBs to restrict sharingDMRS ports with other WDs 22 can be determined based on the selection ofparticular scrambling IDs for the WDs 22. With very few PRBs allocated,the DMRS sequences of two WDs 22 with different scrambling IDs can becorrelated resulting in a bias in the estimated channel. To protect thisbias level, a threshold may be used to restrict the reuse of one or moreDMRS ports.

FIG. 14 is a flow diagram of a process for wireless devices 22 accordingto some embodiments of the disclosure. In one or more embodiments,wireless device 22 such as via one or more of processing circuitry 46,processor 48 and radio interface 44 is configured to transmit and/orreceive (Block S166) a reference signal based on allocated resourcesthat are described herein.

According to one example embodiment, a method in a wireless network thatdetermines resources for DL demodulation reference signal for eachwireless device 22 includes:

a. Dividing all scrambling sequences IDs into multiple non-overlappinggroups;

b. Allocating a group of scrambling sequences IDs to a set of wirelessdevices 22, e.g., users in a cell;

c. Selecting one scrambling sequences ID and configuring this as a firstscrambling sequences ID for all wireless devices 22 in the set;

d. Selecting one scrambling sequences ID randomly from the remaining(without the one selected in the previous step) and configuring this asa second scrambling sequences ID for a wireless device 22 in the set;

e. Trying to use orthogonal demodulation antenna ports to separatelayers and/or wireless devices 22;

f. Allocating the same orthogonal demodulation antenna port to wirelessdevices 22 with good spatial separation if they can use differentscrambling sequences when there are not enough orthogonal demodulationantenna ports available.

As will be appreciated by one of skill in the art, the conceptsdescribed herein may be embodied as a method, data processing system,computer program product and/or computer storage media storing anexecutable computer program. Accordingly, the concepts described hereinmay take the form of an entirely hardware embodiment, an entirelysoftware embodiment or an embodiment combining software and hardwareaspects all generally referred to herein as a “circuit” or “module.” Anyprocess, step, action and/or functionality described herein may beperformed by, and/or associated to, a corresponding module, which may beimplemented in software and/or firmware and/or hardware. Furthermore,the disclosure may take the form of a computer program product on atangible computer usable storage medium having computer program codeembodied in the medium that can be executed by a computer. Any suitabletangible computer readable medium may be utilized including hard disks,CD-ROMs, electronic storage devices, optical storage devices, ormagnetic storage devices.

Some embodiments are described herein with reference to flowchartillustrations and/or block diagrams of methods, systems and computerprogram products. It will be understood that each block of the flowchartillustrations and/or block diagrams, and combinations of blocks in theflowchart illustrations and/or block diagrams, can be implemented bycomputer program instructions. These computer program instructions maybe provided to a processor of a general purpose computer (to therebycreate a special purpose computer), special purpose computer, or otherprogrammable data processing apparatus to produce a machine, such thatthe instructions, which execute via the processor of the computer orother programmable data processing apparatus, create means forimplementing the functions/acts specified in the flowchart and/or blockdiagram block or blocks.

These computer program instructions may also be stored in a computerreadable memory or storage medium that can direct a computer or otherprogrammable data processing apparatus to function in a particularmanner, such that the instructions stored in the computer readablememory produce an article of manufacture including instruction meanswhich implement the function/act specified in the flowchart and/or blockdiagram block or blocks.

The computer program instructions may also be loaded onto a computer orother programmable data processing apparatus to cause a series ofoperational steps to be performed on the computer or other programmableapparatus to produce a computer implemented process such that theinstructions which execute on the computer or other programmableapparatus provide steps for implementing the functions/acts specified inthe flowchart and/or block diagram block or blocks.

It is to be understood that the functions/acts noted in the blocks mayoccur out of the order noted in the operational illustrations. Forexample, two blocks shown in succession may in fact be executedsubstantially concurrently or the blocks may sometimes be executed inthe reverse order, depending upon the functionality/acts involved.Although some of the diagrams include arrows on communication paths toshow a primary direction of communication, it is to be understood thatcommunication may occur in the opposite direction to the depictedarrows.

Computer program code for carrying out operations of the conceptsdescribed herein may be written in an object oriented programminglanguage such as Java® or C++. However, the computer program code forcarrying out operations of the disclosure may also be written inconventional procedural programming languages, such as the “C”programming language. The program code may execute entirely on theuser's computer, partly on the user's computer, as a stand-alonesoftware package, partly on the user's computer and partly on a remotecomputer or entirely on the remote computer. In the latter scenario, theremote computer may be connected to the user's computer through a localarea network (LAN) or a wide area network (WAN), or the connection maybe made to an external computer (for example, through the Internet usingan Internet Service Provider).

Many different embodiments have been disclosed herein, in connectionwith the above description and the drawings. It will be understood thatit would be unduly repetitious and obfuscating to literally describe andillustrate every combination and subcombination of these embodiments.Accordingly, all embodiments can be combined in any way and/orcombination, and the present specification, including the drawings,shall be construed to constitute a complete written description of allcombinations and subcombinations of the embodiments described herein,and of the manner and process of making and using them, and shallsupport claims to any such combination or subcombination.

It will be appreciated by persons skilled in the art that theembodiments described herein are not limited to what has beenparticularly shown and described herein above. In addition, unlessmention was made above to the contrary, it should be noted that all ofthe accompanying drawings are not to scale. A variety of modificationsand variations are possible in light of the above teachings withoutdeparting from the scope of the following claims.

1. A network node, comprising: processing circuitry configured to:allocate resources for a reference signal signaling for a first wirelessdevice, the allocated resources configured to separate, in a slot, atleast one transmission layer of the first wireless device from at leastone transmission layers of a second wireless device by at least one of:scheduling the first wireless device and second wireless device ondifferent reference signal ports that are separated by using the sameresource elements and different code division multiplexing, CDM, codes,the first wireless device and second wireless device having associatedscrambling sequences; scheduling the first wireless device and secondwireless device on at least one shared reference signal port using thesame resource elements and CDM code, the first wireless device andsecond wireless device having different scrambling sequences; schedulingthe first wireless device and second wireless device on differentreference signal ports that are separated by frequency divisionmultiplexing, FDM, using different resource elements and the same CDMcodes, the first and second wireless device having associated scramblingsequences; and scheduling the first wireless device and second wirelessdevice on different reference signal ports that are separated throughboth FDM and CDM by using different resource elements and different CDMcodes, the first wireless device and second wireless device havingassociated scrambling sequences; and the first wireless device scheduledfor a reference signal port combination for one selected from a groupconsisting of: a one front-load reference signal symbol configuration;and a two front-load reference signal symbol configuration.
 2. Thenetwork node of claim 1, wherein the first wireless device and thesecond wireless device having the at least one shared reference signalport are part of a wireless device sub-group, the wireless devicesub-group meeting at least one predefined spatial condition.
 3. Thenetwork node of claim 2, wherein at least one predefined spatialcondition includes a spatial metric associated with each wireless devicewithin the subgroup that meets a predefined criterion with respect toall other wireless devices in the same subgroup.
 4. The network node ofclaim 3, wherein the spatial metric is a measure of an angle of arrival,AoA, between a wireless device and a plane of an antenna array of thenetwork node.
 5. The network node of claim 3, wherein the spatial metricis a measure of a spatial channel of a wireless device within a subgroupwith respect to the network node.
 6. The network node of claim 3,wherein the predefined criterion is associated with a difference ofspatial metrics between two wireless devices that is greater than apredefined threshold.
 7. The network node of claim 3, wherein thepredefined criterion is associated with an absolute value of an innerproduct of the normalized spatial metrics of any two wireless devicesthat is less than a predefined threshold.
 8. The network node of claim1, wherein the allocated resources provide for multi-user multiple-inputmultiple-output, MU-MIMO, transmission.
 9. The network node of claim 1,wherein the number of reference signal ports corresponds to a rank ofthe transmission of the first wireless device.
 10. The network node ofclaim 1, wherein the processing circuitry is further configured todetermine a number of physical resource blocks, PRBs, allocated to thefirst wireless device, the scheduling of the at least one sharedreference port to the first wireless device and second wireless devicebeing based on the determined number of PRBs.
 11. (canceled)
 12. Thenetwork node of claim 1, wherein the processing circuitry is furtherconfigured to: allocate resources for reference signal signaling for aplurality of wireless devices including the first wireless device, theallocated resources configured to separate, in a slot, at least onetransmission layer of each of the plurality of wireless devices fromeach other, respectively.
 13. A method for a network node, the methodcomprising: allocating resources for a reference signal signaling for afirst wireless device, the allocated resources configured to separate,in a slot, at least one transmission layer of the first wireless devicefrom at least one transmission layers of a second wireless device by atleast one of: scheduling the first wireless device and second wirelessdevice on different reference signal ports that are separated by usingthe same resource elements and different code division multiplexing,CDM, codes, the first wireless device and second wireless device havingassociated scrambling sequences; scheduling the first wireless deviceand second wireless device on at least one shared reference signal portusing the same resource elements and CDM code, the first wireless deviceand second wireless device having different scrambling sequences;scheduling the first wireless device and second wireless device ondifferent reference signal ports that are separated by frequencydivision multiplexing, FDM, by using different resource elements and thesame CDM codes, the first and second wireless device having associatedscrambling sequences; and scheduling the first wireless device andsecond wireless device on different reference signal ports that areseparated through both FDM and CDM by using different resource elementsand different CDM codes, the first wireless device and second wirelessdevice having associated scrambling sequences; and the first wirelessdevice scheduled for a reference signal port combination for oneselected from a group consisting of: a one front-load reference signalsymbol configuration; and a two front-load reference signal symbolconfiguration.
 14. The method of claim 13, wherein the first wirelessdevice and the second wireless device having the at least one sharedreference signal port are part of a wireless device sub-group, thewireless device sub-group meeting at least one predefined spatialcondition.
 15. The method of claim 14, wherein at least one predefinedspatial condition includes a spatial metric associated with eachwireless device within the subgroup that meets a predefined criterionwith respect to all other wireless devices in the same subgroup.
 16. Themethod of claim 15, wherein the spatial metric is a measure of an angleof arrival, AoA, between a wireless device and a plane of an antennaarray of the network node.
 17. The method of claim 15, wherein thespatial metric is a measure of a spatial channel of a wireless devicewithin a subgroup with respect to the network node.
 18. (canceled) 19.(canceled)
 20. The method of claim 13, wherein the allocated resourcesprovide for multi-user multiple-input multiple-output, MU-MIMO,transmission.
 21. The method of claim 13, wherein the number ofreference signal ports corresponds to a rank of the transmission of thefirst wireless device.
 22. The method of claim 13, further comprisingdetermining a number of physical resource blocks, PRBs, allocated to thefirst wireless device, the scheduling of the at least one sharedreference port to the first wireless device and second wireless devicebeing based on the determined number of PRBs.
 23. (canceled)
 24. Themethod of claim 13, further comprising allocating resources forreference signal signaling for a plurality of wireless devices includingthe first wireless device, the allocated resources configured toseparate, in a slot, at least one transmission layer of each of theplurality of wireless devices from each other, respectively. 25.(canceled)